System and method for allocating and sharingpage buffers for a flash memory device

ABSTRACT

A flash memory device having a page buffer circuit providing a shared resource between a flash array controller circuit and a user. The page buffer circuit comprises a Plane A and a Plane B, wherein each of the planes A and B is a static random access memory array. The page buffer circuit further comprises a mode control circuit for enabling access to the planes A and B over a host bus in a user mode and access to the planes A and B by the flash array controller in a flash array controller mode.

This is a continuation of application Ser. No. 08/729,339 filed Oct. 16, 1996, now abandoned, which is a continuation of application Ser. No. 08/085,545 filed Jun. 30, 1993, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the field of integrated circuit memory devices. More particularly, this invention relates to a shared page buffer resource for a flash memory device.

2. Art Background

A flash memory device contains a flash cell array for nonvolatile random access data storage in a computer system. Prior flash memory devices usually implement a write control circuit for programming and erasing areas of the flash cell array. The write control circuit typically programs the flash cells by applying a predetermined sequence of program level voltages to the flash cells.

Prior flash memory devices may employ an on-chip programming data buffer to increase programming throughput to the flash cell array. The data buffer enables increased programming speed by buffering a set of programming data. The data buffer enables fast access to the programming data by the write control circuit. The fast access to the programming data enables the write control circuit to amortize the cycling of program level voltages across multiple bytes in the flash cell array.

In such prior flash memory devices, a user typically provides an input/output driver that loads a programming data block into the data buffer. The input/output driver then issues a flash array program command to the write control circuit. Thereafter, the write control circuit accesses the programming data from the data buffer and programs the flash cell array. The input/output driver loads a subsequent programming data block into the data buffer after the write control circuit completes programming from the previous programming data block.

Unfortunately, in such prior flash memory devices, the data buffer is usually not accessible by the input/output driver while the write control circuit programs the flash cell array from the data buffer. As a consequence, the input/output driver is idle while waiting for the completion of the program operation. The idle time of the input/output driver results in reduced programming throughput to the flash memory device.

SUMMARY AND OBJECTS OF THE INVENTION

One object of the present invention is to improve programming throughput to a flash memory device by sharing a page buffer resource between a user and a flash array controller of the flash memory device.

Another object of the present invention is to provide a multiple page plane page buffer for a flash memory device, wherein each page plane functions in either a user mode or a flash array controller mode.

Another object of the present invention is to enable the user to access a page plane when the plane is in the user mode, and to enable the flash array controller to access the page plane when the plane is in the flash array controller mode.

A further object of the present invention is to coordinate allocation of the user mode and the flash array controller mode among the page buffer page planes, such that the flash array controller programs a flash array with data from one page plane while the user loads data into the other page plane.

These and other objects of the invention are provided by a flash memory device having a flash cell array, a flash array controller circuit for programming the flash cell array, and a page buffer circuit providing a shared resource between the flash array controller circuit and a user. The page buffer circuit comprises a set of page planes, wherein the page planes each comprise a static random access memory array. The page buffer circuit further comprises a mode control circuit for enabling access to the page planes over a host bus in a user mode and access to the page planes by the flash array controller in a flash array controller mode. The user mode and the flash array controller mode for each page plane is determined by a plurality of control signals. The flash memory device further comprises an interface circuit for processing commands over the host bus. The interface circuit generates the control signals to allocate the page planes to the user and flash array controller modes according to the requirements of the command from the user.

Other objects, features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description that follows below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements, and in which:

FIG. 1 is a block diagram of a computer system including a central processing unit (CPU), a main memory subsystem, and a set of flash memory devices incorporating the features of an embodiment of the present invention;

FIG. 2 is a block diagram of the flash memory device incorporating the features of an embodiment of the present invention including a flash cell array, an interface circuit, a flash array controller, a set of page buffers, a set of control register circuits, and a set of read/write path circuitry;

FIG. 3 is a block diagram illustrating features of an embodiment of the present invention including the interface circuit comprising a command state machine, a data/address queue, an operation queue, and a set of block status registers (BSR);

FIG. 4 is a block diagram illustrating features of an embodiment of the present invention including the page buffer circuit which is comprised of two separate 256 by 8 bit static random access memory (SRAM) planes and remnant bits;

FIG. 5 illustrates features of an embodiment of the present invention including the architecture of the Plane A and the Plane B which are each comprised of two 128×8 bit columns (columns A and B) and one 128×3 bit column (column C);

FIG. 6 illustrates features of an embodiment of the present invention including the modes of the page buffer circuit wherein the modes comprise modes 0 through 7;

FIG. 7 illustrates features of an embodiment of the present invention including the address mapping of the page buffer circuit for modes 1-7;

FIG. 8 illustrates features of an embodiment of the present invention including the address bit fields for accessing the page buffer circuit, wherein the address bits shown are transferred over the FAC address bus, the IC address bus, or the FAC program counter bus according to the mode;

FIG. 9 illustrates features of an embodiment of the present invention including the FAC plane assignment of the Plane A and the Plane B for accesses by the flash array controller;

FIG. 10 illustrates features of an embodiment of the present invention including the assignment of the Plane A and the Plane B for accesses by the interface circuit;

FIG. 11 illustrates features of an embodiment of the present invention including a truth table showing the states of the plane₋₋ B select which is generated by the column select circuit;

FIG. 12 illustrates features of an embodiment of the present invention including a truth table showing the states of the plane₋₋ A select which is generated by the column select circuit;

FIG. 13 illustrates features of an embodiment of the present invention including the output data aligner circuit which transfers the output data from the Plane A and the Plane B over the FAC instruction bus, the FAC data bus and the page buffer data bus according to the mode;

FIG. 14 illustrates features of an embodiment of the present invention including a truth table for the output data aligner circuit that illustrates the data transferred over the IC data bus according to the mode;

FIG. 15 illustrates features of an embodiment of the present invention including a truth table for the output data aligner circuit showing the data transferred over the FAC data bus according to the mode;

FIG. 16 illustrates features of an embodiment of the present invention including a truth table for the output data aligner circuit showing the data transferred over the FAC instruction bus according to the mode;

FIG. 17a illustrates features of an embodiment of the present invention including a global status register which contains status bits that indicate the status of the page buffer circuit for the flash memory device;

FIG. 17b illustrates features of an embodiment of the present invention a program sequence to the flash array that employs the page buffer circuit.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of a computer system 300. The computer system 300 is comprised of a central processing unit (CPU) 302, a main memory subsystem 304, and a set of flash memory devices 310-314. The CPU 302 communicates with the main memory subsystem 304 and the flash memory devices 310-314 over a host bus 306.

The flash memory devices 310-314 provide random access non volatile large scale data storage for the computer system 300. The CPU 302 reads the contents of the flash memory devices 310-314 by generating read memory cycles over the host bus 306. The CPU 302 writes to the flash memory devices 310-314 by transferring write commands and write data blocks to the flash devices 310-314 over the host bus 306.

FIG. 2 is a block diagram of the flash memory device 310. The flash memory device 310 is comprised of a flash cell array 20, an interface circuit 40, a flash array controller 50, a set of page buffer circuit 70, a set of control register circuits 80-85, and a set of read/write path circuitry 30.

The flash cell array 20 provides random access non volatile large scale data storage. For one embodiment, the flash cell array 20 is arranged as a set of 32 flash array blocks. Each flash array block provides 64k bytes of data storage.

The flash memory device 310 is shown coupled to the host bus 306. The host bus 306 comprises an user address bus 102, a user data bus 104, and a user control bus 106.

The read/write path circuitry 30 comprises read and write path circuitry for accessing the flash array 20. For example, the read/write path circuitry 30 includes row and column address decoding circuitry for the flash array 20. The read/write path circuitry 30 also includes redundancy circuitry for overriding addresses if a bad flash cell is detected in the flash array 20. The read/write path circuitry 30 also includes mini array circuitry for generating reference flash bits, and sense path circuitry for comparing the reference flash bits to bits from the flash array 20 to determine whether the bits are logic state 1 or logic state 0.

The read/write path circuitry 30 also includes multiplexer circuitry for selecting between bits from the flash array 20 and redundant bits, as well as multiplexer circuitry for selecting between the high and low bytes of the flash array 20 to provide for 8 bit and 16 bit accesses. The read/write path circuitry 30 includes output buffer circuitry for driving data from the flash array 20 over output pads of the flash memory device 310.

The read/write path circuitry 30 includes address transition detection circuitry. The address transition detection circuitry generates control pulses when address transitions are detected. The control pulses are employed to speed column charging at the outputs of the flash array 20 before data is ready.

The read/write path circuitry 30 includes high voltage circuitry for accessing the flash array 20. For example, the read/write path circuitry 30 includes VPX switching circuitry for setting the wordline voltage for programming data into the flash array 20, and VPY generator circuitry for setting the programming load line. The read/write path circuitry 30 also includes VSI generator circuitry for setting the source voltage of unselected blocks of the flash array 20 during programming.

The read/write path circuitry 30 also includes digital to analog conversion circuits for generating reference voltage levels for program verify operations, as well as erase verify and post erase repair operations. The read/write path circuitry 30 also includes VPS switch circuitry for setting the source voltage level to VPP during erase operations.

The control register circuits 80-85 contain sets of specialized control registers and associated circuitry for controlling a read/write path 30. The specialized control registers are programmed and accessed over a central control bus 100.

The interface circuit 40 enables access of the flash cell array 20 over the host bus 306 by receiving and processing commands over the host bus 306. The interface circuit 40 receives commands over the user data bus 104, verifies the commands, and queues the commands to the flash array controller 50 over a queue bus 41. Thereafter, the flash array controller 50 executes the command using the appropriate portion of the flash memory device 310.

The flash array controller 50 is a specialized reduced instruction set processor for performing write operations on the flash array 20. The flash array controller 50 includes an arithmetic logic unit, general purpose registers, a control store and a control sequencer. The flash array controller 50 uses the commands received over the queue bus 41 to dispatch to the appropriate location of the control store to execute the command.

A control access circuit 60 enables both the interface circuit 40 and the flash array controller 50 to access the control register circuits 80-85 over the central control bus 100. During a normal mode of the flash memory device 310, the flash array controller 50 controls the control access circuit 60 and accesses the control register circuits 80-85 over the central control bus 100.

The flash array controller 50 writes to the specialized control registers by transferring a write control signal, and a register address along with corresponding write data to the control access circuit 60 over a bus 52. The control access circuit 60 then generates a write cycle over the central control bus 100 to program the addressed specialized control register. The flash array controller 50 reads the specialized control registers by transferring a register address and read control signal to the control access circuit 60 over the bus 52. The control access circuit 60 then generates a read access cycle over the central control bus 100 to read the addressed specialized control register.

The control register circuit 80 contains specialized control registers and circuitry for controlling the high voltage circuitry of the read/write path 30 according to a set of control signals 90. The high voltage control registers include source switch interface registers, interface registers for controlling VPX and VPIX multiplexers, VPP/VCC switch interface registers, interface registers for controlling reference generators, multiplexers and comparators, and programming data path interface registers.

The control register circuit 81 contains control registers and circuitry for controlling special column access circuitry of the read/write path 30 according to a set of control signals 91. The special column access control registers include mini-array interface registers, redundancy interface registers, imprint interface registers, and content addressable memory interface registers.

The control register circuit 82 contains a set of read only registers for sensing and latching a set of status signals 92 from the read/write path 30. The status signals 92 include the outputs of TTL buffers corresponding to input pads of the flash memory device 310, outputs of the sense amplifiers for the flash cell array 20, page buffer counter outputs, outputs of the comparators in the read/write path 30, and the flash array controller 50 program counter.

The control register circuit 83 contains control registers and circuitry for controlling the read path of the read/write path 30 according to a set of control signals 93. The read path control registers include automatic transition detection interface registers, sensing interface registers, x, y, and z path interface registers, and c path interface registers.

The control register circuit 84 contains registers for controlling a set of test modes of the page buffer circuit 70. The control registers in the control register circuit 84 generate a set of test mode test mode control signals 94. The control registers in the control register circuit 84 are programmed over the central control bus 100 by the flash array controller 50 or the interface circuit 40.

The control register circuit 85 contains registers for controlling special test features of the flash memory device 310 according to a set of control signals 95. The special test registers include test mode access registers, VPP capture registers, ready and busy modifier registers, and address allocation registers.

The interface circuit 40 controls an input address multiplexer 35 to select an input address 36 for the read/write path 30. The selected input address 36 is either the address sensed by TTL buffers (not shown) on the user address bus 102, or a latched address 37 from the interface circuit 40.

The interface circuit 40 controls an output data multiplexer 45 to select a source for output data transfer over the user data bus 104. The selected output data is either flash array data 46 from the read/write path 30, page buffer data 47 from the page buffer circuit 70, or block status register (BSR) data 48 from a set of block status registers contained within the interface circuit 40.

The CPU 302 reads the flash cell array 20 by transferring addresses over the user address bus 102 while signaling read cycles over the user control bus 106. The interface circuit 40 detects the read cycles and causes the input address multiplexer 35 to transfer the addresses from the user address bus 102 through to the x and y decode circuitry of the read/write path 30. The interface circuit 40 also causes the output data multiplexer 45 to transfer the addressed read data from the read/write path 30 over the user data bus 104.

The CPU 302 writes data to the flash cell array 20 by generating I/O write cycles over the host bus 306 to transfer programming data blocks to the page buffer circuit 70. The interface circuit 40 verifies the write command, and queues the write command to the flash array controller 50. The flash array controller 50 executes the write command by reading the programming data from the page buffers over a controller bus 51, and by programming the appropriate areas of the flash array 20.

The flash array controller 50 implements algorithms for sequencing the high voltage circuitry of the read/write path 30 in order to apply charge to the flash cells of the flash cell array 20 and remove charge from the flash cells of the flash cell array 20. The flash array controller 50 controls the high voltage circuitry and addresses the flash array 20 by accessing the control register circuits 80-85 over the central control bus 100.

The read/write path 30 includes source switch circuitry for applying the appropriate voltage levels to the flash cell array 20 for an erase function. The read/write path 30 also includes program load circuitry for driving program level voltages onto the bit lines of the flash cell array 20 during a programming function.

The interface circuit 40 contains 32 block status registers. Each block status register corresponds to one of the blocks of the flash cell array 20. The flash array controller 50 maintains status bits in the block status registers to indicate the status of each block of the flash cell array 20. The CPU 302 reads the contents of the block status registers over the host bus 306.

FIG. 3 is a block diagram of the interface circuit 40. The interface circuit 40 is comprised of a command state machine 210, a data/address queue 212, an operation queue 214, and a set of block status registers (BSR) 216.

The command state machine 210 receives commands from the CPU 302 over the host bus 306. The commands from the CPU 302 include commands for performing program and erase operations on individual bytes or words of the flash array 20, as well as commands for performing program and erase operations with data stored in the page buffer circuit 70.

The command state machine 210 verifies the commands, and transfers commands and associated parameters to the flash array controller 50 through the operation queue 214. The command state machine 210 also transfers control signals over a command bus 220 to control a set of modes for the page buffer circuit 70.

The command state machine 210 processes commands for reading the status registers of the BSR 216. The command state machine 210 selects the status registers of the BSR 216 by transferring addresses and control signals to the BSR 216 over a command bus 220. The status registers of the BSR 216 include a global status register that indicates the status of the page buffer circuit 70.

The operation queue 214 transfers the latched addresses 37 from the data/address queue 212 to the input multiplexer 35. The operation queue 214 also transfers the latched array data 38 from the data/address queue 212 to the read/write path 30. The operation queue 214 transfers the verified commands and associated parameters to the flash array controller 50 over the queue bus 41.

The BSR 216 contains a block status register for each of the flash array blocks of the flash array 20. Each block status register in the BSR 216 stores status bits that provide block specific status information to a user.

The flash array controller 50 maintains the status bits in the status registers of the BSR 216. The flash array controller 50 accesses the status registers of the BSR 216 over the central control bus 100. The flash array controller 50 performs both reads and writes to the BSR 216 over the central control bus 100.

The interface circuit 40 enables read access of the status registers over the host bus 306. The CPU 302 reads the status registers of the BSR 216 by transmitting read status register commands to the command state machine 210 over the host bus 306. The read block status register commands include a status register address for selecting the 32 block status registers in the BSR 216.

The command state machine 210 transfers the status register address over the command bus 220 to select the status registers the BSR 216. The contents of the selected status register are transferred from the BSR 216 to the output multiplexer 45 over the BSR data bus 48. The command state machine 210 causes the output multiplexer 45 to transfer the status register read data on the BSR data bus 48 over the user data bus 104.

FIG. 4 is a block diagram illustrating the page buffer circuit 70. The page buffer circuit 70 is comprised of two separate 256 by 8 bit static random access memory (SRAM) planes. The two SRAM planes comprise a Plane A 310 and a Plane B 320.

The command bus 220 is shown comprising an interface circuit (IC) address bus 222, a set of IC control signals 224, and IC byte signal 344, and an initialize page buffer signal 331. The controller bus 51 is shown comprising a flash array controller (FAC) data bus 232, an FAC address bus 236, an FAC program counter bus 238, an FAC instruction bus 230, and a set of FAC control signals 234.

The rows of the Plane A 310 and the Plane B 320 are addressed over the IC address bus 222, the FAC address bus 236, and the FAC program counter bus 238. The command state machine 210 addresses the Plane A 310 and the Plane B 320 over the IC address bus 222. The flash array controller 50 addresses the Plane A 310 and the Plane B 320 during data accesses over the FAC address bus 236. The flash array controller 50 addresses the Plane A 310 and the Plane B 320 during instruction fetches over the FAC program counter bus 238.

The page buffer circuit 70 is also comprised of a mode detector circuit 300, a column select circuit 302, a pair of input multiplexers 304 and 306, and an output data aligner circuit aligner 315.

FIG. 5 illustrates the architecture of the Plane A 310 and the Plane B 320. The Plane A 310 and the Plane B 320 are each comprised of two 128×8 bit columns (col. A and col. B) and one 128×3 bit column (col. C). The column A and B store byte or word values. The column C stores remnant bits for special test modes of the page buffer circuit 70.

FIG. 6 illustrates the modes of the page buffer circuit 70, for one embodiment. The operating modes of the page buffer circuit 70 comprise modes 0 through 7.

In mode 0, access to the page buffer circuit 70 is disabled. The page buffer circuit 70 is not accessible by the user or the flash array controller 50.

In mode 1, the page buffer circuit 70 functions as a control store for the flash array controller 50 in a special test mode. The flash array controller 50 fetches an instruction by transferring an instruction address to the page buffer circuit 70 over the FAC address bus 236. The flash array controller 50 receives the corresponding instruction from the page buffer circuit 70 over the FAC instruction bus 230.

In mode 2, the interface circuit 40 reads the page buffer circuit 70 in user mode. The interface circuit 40 receives a read page buffer command over the host bus 306. The read page buffer command specifies a read address for the page buffer circuit 70. The command state machine 210 transfers the read address to the page buffer circuit 70 over the IC address bus 222. The page buffer circuit 70 transfers the corresponding read data over the page buffer data bus 47. The interface circuit 40 causes the multiplexer 45 to transfer the read data over the user data bus 104.

In mode 3, the interface circuit 40 writes to the page buffer circuit 70 in user mode. A user mode write to the page buffer circuit 70 is either a write byte/word transaction or a write sequential transaction. The write byte/word transaction to the page buffer circuit 70 begins when the interface circuit 40 receives a write page buffer command over the host bus 306. The write page buffer command specifies a write address for the page buffer circuit 70, as well as a write data value. The command state machine 210 transfers the write address to the page buffer circuit 70 over the IC address bus 222. The page buffer circuit 70 receives the write data value over the user data bus 104.

A write sequential transaction to the page buffer circuit 70 begins when the interface circuit 40 receives a write page buffer sequential command over the host bus 306. The write page buffer sequential command specifies a starting address for the page buffer circuit 70, as well as a byte count. The interface circuit 40 contains a write counter circuit (not shown). The write counter circuit is loaded with the byte count upon receipt of the write page buffer sequential command. Thereafter, the write counter circuit counts down as the page buffer circuit 70 receives write data values over the user data bus 104. While the write data values are being received, the command state machine 210 addresses the page buffer circuit 70 over the IC address bus 222 according to the write counter circuit.

In mode 4, the flash array controller 50 reads from the page buffer circuit 70 in user mode. For example, the flash array controller 50 reads programming data from the page buffer circuit 70 during a program with page buffer operation. The flash array controller 50 addresses the page buffer circuit 70 over the FAC address bus 236. The flash array controller 50 receives the corresponding programming data from the page buffer circuit 70 over the FAC data bus 232.

In mode 5, the flash array controller 50 writes to the page buffer circuit 70 in user mode. The flash array controller 50 addresses the page buffer circuit 70 over the FAC address bus 236, and transfers the corresponding write data to the page buffer circuit 70 over the FAC data bus 232.

In mode 6, the interface circuit 40 reads the page buffer circuit 70 in a special test mode having an extended space. The interface circuit 40 receives a read page buffer command specifying a read address over the host bus 306. The command state machine 210 transfers the read address to the page buffer circuit 70 over the IC address bus 222, and the page buffer circuit 70 transfers the corresponding read data over the page buffer data bus 47.

In mode 7, the interface circuit 40 writes to the page buffer circuit 70 in the special test mode having the extended space. The interface circuit 40 receives a write page buffer command specifying a write address and a write data value over the host bus 306. The command state machine 210 transfers the write address to the page buffer circuit 70 over the IC address bus 222. The page buffer circuit 70 receives the write data value over the user data bus 104.

FIG. 7 illustrates the address mapping of the page buffer circuit 70 for each mode. In mode 1, the whole page buffer comprising columns A, B and C of the Plane A 310 and columns A, B and C of the Plane B 320 is mapped into a 256 by 19 bit control store. In mode 1, the page buffer circuit 70 functions as a 256 entry control store for the flash array controller 50.

In modes 2 through 5, the page buffer circuit 70 is mapped into two independent planes (PLANE A and PLANE B). PLANE A and PLANE B are each 256 by 8 bits. PLANE A and PLANE B may be accessed in eight bit mode or in sixteen bit mode by either the interface circuit 40 or the flash array controller 50. In modes 2 through 5, the interface circuit 40 coordinates access to PLANE A and PLANE B according to commands received over the host bus 306. The interface circuit 40 ensures that both the interface circuit 40 and the flash array controller 50 do not access the same plane.

In modes 6 and 7, PLANE A and PLANE B are mapped into one contiguous extended memory space. The extended memory space includes columns A, B and C of the Plane A 310 and columns A, B and C of the Plane B 320. Modes 6 and 7 comprise special test modes for testing the page buffer circuit 70.

FIG. 8 illustrates the address bit fields for accessing the page buffer circuit 70. The address bits shown are transferred over the FAC address bus 236, the IC address bus 222, or the FAC program counter bus 238 according to the mode.

Address bit A9 functions as a remnant data select for selecting column C of the Plane A 310 and the Plane B 320 in modes 1, and 6-7. Address bit A8 functions as a plane select for selecting either the Plane A 310 or the Plane B 320. Address bits A7 through A1 select a row of the Plane A 310 and the Plane B 320. Address bit A0 selects either the high byte or the low byte of a row.

The mode detector circuit 300, shown in FIG. 4, determines the mode for the page buffer circuit 70. The mode detector circuit 300 generates a plane₋₋ A mode 333 and a plane₋₋ B mode 335. The plane ₋₋ A mode 333 and the plane₋₋ B mode 335 each comprise three bits. The plane₋₋ A mode 333 determines the mode for the Plane A 310. The plane₋₋ B mode 335 determines the mode for the Plane B 320.

The mode detector circuit 300 generates the plane ₋₋ A mode 333 and the plane₋₋ B mode 335 according to the FAC control signals 234 from the flash array controller 50, the IC control signals 224 from the command state machine 210, and the test mode control signals 94.

The FAC control signals 234 comprise bit 7 of the FAC program counter, bit 8 of the FAC address bus 236, and the current FAC instruction.

The IC control signals 224 comprise bit 8 of the IC address bus 222, an IC plane status signal, and an IC plane select signal. The IC control signals 224 also comprise an FAC plane status signal, an FAC plane select signal, a single byte/word write signal, and a write sequential signal.

The test mode test mode control signals 94 include an FAC control store enable signal, a test mode extend signal, and a 2 bit FAC override signal. The FAC control store enable signal determines whether the page buffer circuit 70 functions as a control store for the flash array controller 50. The test mode extend signal determines whether the page buffer circuit 70 functions in the extended modes 6-7.

FIG. 9 illustrates the assignment of the Plane A 310 and the Plane B 320 for accesses by the flash array controller 50. The FAC plane assignment is determined by the FAC plane select signal, the FAC plane status signal, and the FAC override signal.

If bits 0 and 1 of the FAC override signal are both zero, the FAC plane select signal determines whether the flash array controller 50 is allocated the Plane A 310 or the Plane B 320. The FAC plane status signal indicates whether the plane determined by the FAC plane select signal is available.

The FAC override signal overrides the normal plane assignment mechanism and allocates either the Plane A 310 or the Plane B 320 to the flash array controller 50.

FIG. 10 illustrates the assignment of the Plane A 310 and the Plane B 320 for accesses by the interface circuit 40. The plane assignment for the interface circuit 40 is determined by the IC plane status signal, the IC plane select signal, and the test mode extend signal.

If the test mode extend signal is asserted, the interface circuit 40 accesses to the Plane A 310 and the Plane B 320 including the remnant bits in the extended memory space.

If the test mode extend signal is not asserted, the IC plane select signal determines whether the interface circuit 40 is allocated the Plane A 310 or the Plane B 320. The IC plane status signal indicates whether the plane selected by the IC plane select signal is available.

The command state machine 210 generates the IC plane status signal, the IC plane select signal, the FAC plane status signal, and the FAC plane select signal to allocate the Plane A 310 and the Plane B 320 to the flash array controller 50 and the interface circuit 40. The command state machine 210 generates the IC and FAC plane status and plane select signals to ensure that the Plane A 310 is not concurrently allocated to both the flash array controller 50 and the interface circuit 40. Similarly, the command state machine 210 generates the IC and FAC plane status and plane select signals to ensure that the Plane B 320 is not concurrently allocated to both the flash array controller 50 and the interface circuit 40.

The mode detector circuit 300 also generates an FAC byte signal 352. The FAC byte signal 352 indicates whether the flash array controller 50 is performing a byte or a word access to the page buffer circuit 70. The mode detector circuit 300 determines the byte or word access by decoding the current FAC instruction.

The column select circuit 302 receives the plane₋₋ A mode 333 and the plane ₋₋ B mode 335, and the FAC byte signal 352 from the mode detector circuit 300. The column select circuit 302 also receives an IC byte signal 344. The IC byte signal 344 indicates whether the user is performing a byte or a word access of the page buffer circuit 70. Byte or word accesses from the user are determined by a control input pin coupled to the user control bus 106.

The column select circuit 302, shown in FIG. 4, receives bit 0 of the IC address bus 222 over a signal line 346, and bit 9 of the IC address bus 222 over a signal line 348. The column select circuit 302 receives bit 0 of the FAC address bus 236 over a signal line 350. In addition, the column select circuit 302 receives an initialize page buffer signal 331.

The column select circuit 302 generates a three bit plane₋₋ A select 337 and a three bit plane₋₋ B select 339. The plane₋₋ A select 337 provides column select signals for the Plane A 310. The plane₋₋ B select 339 provides column select signals for the Plane B 320.

FIG. 11 is a truth table showing the states of the plane₋₋ B select 339 generated by the column select circuit 302. The plane₋₋ B select 339 is determined by the plane₋₋ B mode 335, the FAC override signal, the initialize page buffer (INIT PB) signal 331, the FAC address bit 0, the IC address bits 9 and 0, the FAC byte signal 352, and the IC byte signal 344.

FIG. 12 is a truth table showing the states of the plane₋₋ A select 337 generated by the column select circuit 302. The plane₋₋ A select 337 is determined by the plane₋₋ A mode 333, the FAC override signal, the initialize page buffer signal 331, the FAC address bit 0, the IC address bits 9 and 0, the FAC byte signal 352, and the IC byte signal 344. The Plane A 310 receives input data through the input multiplexer 304. The input multiplexer 304 receives data over the FAC data bus 232 from the flash array controller 50, and over the user data bus 104 from the user. The input multiplexer 304 is controlled by the plane₋₋ A mode 333 and the initialize page buffer signal 331.

In modes 2, 3, 6, and 7, the plane₋₋ A mode 333 causes the input multiplexer 304 to transfer input data from the user data bus 104 to the input of the Plane A 310. In modes 4 and 5, the plane₋₋ A mode 333 causes the input multiplexer 304 to transfer input data from the FAC data bus 232 to the input of the Plane A 310.

The Plane B 320 receives input data through the input multiplexer 306. The input multiplexer 306 receives data over the FAC data bus 232 from the flash array controller 50, and over the user data bus 104 from the user. The input multiplexer 306 is controlled by the plane₋₋ B mode 335 and the initialize page buffer signal 331.

In modes 2, 3, 6, and 7, the plane₋₋ B mode 335 causes the input multiplexer 306 to transfer input data from the user data bus 104 to the input of the Plane B 320. In modes 4 and 5, the plane₋₋ B mode 335 333 causes the input multiplexer 306 to transfer input data from the FAC data bus 232 to the input of the Plane B 320.

The Plane A 310 transfers output data over a plane₋₋ A data bus 340. The plane₋₋ A data bus 340 comprises 19 bits of data. The plane₋₋ A data bus 340 includes a high byte from column A, a low byte from column B, and 3 remnant bits from column C.

The Plane B 320 transfers output data over a plane₋₋ B data bus 342. The plane₋₋ B data bus 342 comprises 19 bits of data including a high byte from column A, a low byte from column B, and 3 remnant bits from column C.

FIG. 13 illustrates the output data aligner circuit 315. The output data aligner circuit 315 transfers the output data from the Plane A 310 and the Plane B 320 over the FAC instruction bus 230, the FAC data bus 232 and the page buffer data bus 47 according to the plane₋₋ A mode 333, the plane₋₋ B mode 335, the plane₋₋ A select 337, and the plane₋₋ B select 339.

The output data aligner circuit 315 receives output data over the plane₋₋ A data bus 340 and the plane₋₋ B data bus 342. The output data aligner circuit 315 is comprised of a multiplexer control circuit 360, a decode circuit 372, along with a set of multiplexers 362-370.

The multiplexer control circuit 360 receives the plane₋₋ A select 337, the plane₋₋ B select 339, the plane₋₋ A mode 333, and the plane₋₋ B mode 335. The multiplexer control circuit 360 generates a pair of multiplexer control signals 380 and 381.

The decode circuit 372 receives the plane₋₋ A mode 333 and the plane₋₋ B mode 335. The decode circuit 372 generates a multiplexer control signal 382.

The multiplexer 362 selectively couples the Plane A data bus 340 and the Plane B data bus 342 to inputs of the multiplexer 366. The Plane A data bus 340 carries the high byte, the low byte and the remnant bits from the Plane A 310. The Plane B data bus 342 carries the high byte, the low byte and the remnant bits from the Plane B 320. The multiplexer 362 selectively couples the Plane A data bus 340 and the Plane B data bus 342 to the multiplexer 366 under control of the multiplexer control signal 380.

The multiplexer 366 selectively couples the received high byte, the received low byte and the received remnant bits to the page buffer data bus 47 under control of the multiplexer control signal 380. For one embodiment, the page buffer data bus 47 comprises 16 bits.

The multiplexer 364 selectively couples the Plane A data bus 340 and the Plane B data bus 342 to inputs of the multiplexer 368. The multiplexer 364 selectively couples the Plane A data bus 340 and the Plane B data bus 342 to the multiplexer 368 under control of the multiplexer control signal 381.

The multiplexer 368 selectively couples the received high byte, the received low byte and the received remnant bits to the FAC data bus 232 under control of the multiplexer control signal 381. For one embodiment, the FAC data bus 232 comprises 16 bits.

The multiplexer 370 receives output data from the Plane A 310 over the plane₋₋ A data bus 340, and output data from the Plane B 320 over the plane₋₋ B data bus 342. The multiplexer 370 selectively couples the Plane A or Plane B output data to the FAC instruction bus 230 under control of the multiplexer control signal 382. For one embodiment, the FAC instruction bus 230 comprises 19 bits including the high and low bytes from columns A and B and the three remnant bits from column C.

FIG. 14 is a truth table for the output data aligner circuit 315 that illustrates the data transferred over the page buffer data bus 47. The data transferred over the page buffer data bus 47 is determined by the plane₋₋ A mode 333, the plane₋₋ A select 337, the plane₋₋ B mode 335, and the plane₋₋ B select 339.

FIG. 15 is a truth table for the output data aligner circuit 315 showing the data transferred over the FAC data bus 232. The data transferred over the FAC data bus 232 is determined by the plane₋₋ A mode 333, the plane₋₋ A select 337, the plane₋₋ B mode 335, and the plane₋₋ B select 339.

FIG. 16 is a truth table for the output data aligner circuit 315 showing the data transferred over the FAC instruction bus 230. The data transferred over the FAC instruction bus 230 is determined by the plane₋₋ A mode 333 and the plane₋₋ B mode 335.

FIG. 17a illustrates a global status register for the flash memory device 310. The global status register contains status bits that indicate the status of the page buffer circuit 70. The global status register is contained within the interface circuit 40. The user reads the global status register over the host bus 306 to determine the status of the Plane A 310 and the Plane B 320 during modes 2-5.

The global status registers stores a page buffer available bit (PB AVAIL) a page buffer select bit (PB SEL) and a page buffer status bit (PB STAT).

The page buffer available bit indicates whether one of the page buffer planes (Plane A or B) is available for user access. A page buffer plane is available for user access when one of the page buffer planes is not allocated to the flash array controller 50.

The page buffer select bit indicates which of the page buffer planes (Plane A or B) is allocated for user access.

The page buffer status bit indicates whether the page buffer plane indicated by the page buffer select bit is available for user access.

FIG. 17b illustrates a program sequence for the flash array 20 that employs the page buffer circuit 70. At time 1, the user reads the global status registers to determine whether a page buffer plane is available for user access. For the example shown, the global status register indicates that Plane A is available for user access.

Thereafter, the user transfers program data to the allocated Plane A by transferring a write sequential command followed by a write data block over the user data bus 306. The page buffer circuit automatically routes the write data block into the Plane A 310 as described above.

At time 2, the user issues a program with page buffer command to the flash memory device 310. The command state machine 210 receives the program with page buffer command, queues the program with page buffer command to the flash array controller 50, and generates the IC control signals 224 to allocate the Plane A 310 to the flash array controller 50 and the Plane B 320 to user access. Thereafter, the flash array controller 50 programs the flash array 20 with the data from Plane A.

Between times 2 and 3, the user loads Plane B while the flash array controller 50 programs from Plane A. The user transfers program data to the allocated Plane B by transferring a write sequential command followed by a write data block over the user data bus 306. The page buffer circuit automatically routes the write data block into the Plane B 320.

At time 3, the user issues a program with page buffer command to the flash memory device 310. The command state machine 210 receives the program with page buffer command, queues the program with page buffer command to the flash array controller 50, and generates the IC control signals 224 to allocate the Plane B 320 to the flash array controller 50 and the Plane A 310 to user access after the flash array controller 50 completes the program operation from plane A. Thereafter, the flash array controller 50 programs the flash array 20 with the data from Plane B while the user loads Plane A with a new program data block.

The user may swap allocation of the page buffer planes A and B by issuing a swap page buffer command. The swap page buffer command causes the command state machine 210 to switch the allocation of planes A and B between the flash array controller 50 and user access.

In the foregoing specification the invention has been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded as illustrative rather than a restrictive sense. 

What is claimed is:
 1. A flash memory device, comprising:a page buffer circuit configured to be coupled to a host bus through a first port and to an internal bus through a second port and comprising a plurality of page planes and a mode control circuit configured to enable access to the page planes over the host bus in a user mode and to the page planes over the internal bus in a flash array controller mode, the user mode and the flash array controller mode determined by at least one control signal; an interface circuit coupled to the page buffer circuit and to the host bus, the interface circuit configured to receive a command over the host bus and to generate the at least one control signal to allocate the page planes to the user and flash array controller modes according to the command; and a flash array controller circuit coupled to the page buffer circuit over the internal bus and configured to access the page buffer circuit in the flash array controller mode.
 2. The flash memory device of claim 1, wherein the command comprises a write page buffer sequential command, the write page buffer sequential command causing the interface circuit to allocate a first page plane of the page planes to the user mode and receive a write data block over the host bus and transfer the write data block into the first page plane.
 3. The flash memory device of claim 2, wherein after the write page buffer sequential command is received, the command comprises a program with page buffer command, the program with page buffer command causing the interface circuit to allocate the first page plane to the flash array controller mode.
 4. The flash memory device of claim 3, wherein if a second page plane of the page planes is not allocated to the flash array controller mode, the interface circuit allocates the second page plane to the user mode and receives a next write page buffer sequential command and a next write data block over the host bus and transfers the next write data block into the second page plane.
 5. The flash memory device of claim 1, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a write page buffer sequential command, such that the interface circuit allocates the page plane A to the user mode and receives a write data block over the host bus and transfers the write data block into the page plane A.
 6. The flash memory device of claim 5, wherein a subsequent command received over the host bus comprises a program with page buffer command, such that the interface circuit allocates the page plane A to the flash array controller mode.
 7. The flash memory device of claim 6, wherein the interface circuit allocates the page plane B to the user mode if the page plane B is not allocated to the flash array controller mode.
 8. The flash memory device of claim 1, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a write page buffer sequential command, such that the interface circuit allocates the page plane B to the user mode and receives a write data block over the host bus and transfers the write data block into the page plane B.
 9. The flash memory device of claim 8, wherein a subsequent command received over the host bus comprises a program with page buffer command, such that the interface circuit allocates the page plane B to the flash array controller mode.
 10. The flash memory device of claim 9, wherein the interface circuit allocates the page plane A to the user mode if the page plane A is not allocated to the flash array controller mode.
 11. The flash memory device of claim 1, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a swap page buffer command, the swap page buffer command causing the interface circuit to swap the user mode and the flash array controller mode between the page plane A and the page plane B.
 12. A method for allocating a page buffer resource in a flash memory device, comprising the steps of:receiving a write page buffer sequential command over a host bus and allocating a first page plane of the page buffer resource to a user mode such that the first page plane is accessible over the host bus in the user mode: receiving a write data block over the host bus and transferring the write data block to the first page plane: receiving a program with page buffer command and allocating the first page plane to a flash array controller mode such that the first page plane is accessible by a flash array controller over an internal bus in the flash array controller mode, and allocating a second page plane of the page buffer resource to the user mode if the second page plane is not allocated to the flash array controller mode, wherein the page buffer resource is coupled to the host bus through a first port and to the internal bus through a second port.
 13. The method of claim 12, further comprising the steps of receiving a second write page buffer sequential command over the host bus, and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 14. The method of claim 12, further comprising the step of programming a flash cell array with the write data block from the first page plane while receiving a second write page buffer sequential command over the host bus and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 15. A method for allocating a page buffer resource in a flash memory device, wherein the page buffer resource comprises a page plane A and a page plane B, and the page buffer resource is coupled to a host bus through a first port and to an internal bus through a second port the method comprising the steps of:receiving a write page buffer sequential command over the host bus and allocating the page plane A of the page buffer resource to a user mode such that the page plane A is accessible over the host bus in the user mode: receiving a write data block over the host bus and transferring the write data block to the page plane A: receiving a program with page buffer command and allocating the page plane A to a flash array controller mode such that the page plane A is accessible by a flash array controller over the internal bus in the flash array controller mode, and receiving a swap page buffer command over the host bus, and swapping the user mode and the flash array controller mode between the page plane A and the page plane B.
 16. A circuit for allocating a page buffer resource in a flash memory device, comprising:a circuit for receiving a write page buffer sequential command over a host bus and allocating a first page plane of the page buffer resource to a user mode, such that the first page plane is accessible over the host bus in the user mode; a circuit for receiving a write data block over the host bus and transferring the write data block to the first page plane; a circuit for receiving a program with page buffer command and allocating the first page plane to a flash array controller mode, such that the first page plane is accessible by a flash array controller over an internal bus in the flash array controller mode; and a circuit for allocating a second page plane of the page buffer resource to the user mode if the second page plane is not allocated to the flash array controller mode, wherein the page buffer resource is coupled to the host bus through a first port and to the internal bus through a second port.
 17. The circuit of claim 16, further comprising a circuit for receiving a second write page buffer sequential command over the host bus, and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 18. The circuit of claim 16, further comprising a circuit for programming a flash cell array with the write data block from the first page plane while receiving a second write page buffer sequential command over the host bus and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 19. A circuit for allocating a page buffer resource in a flash memory device, wherein the page buffer resource comprises a page plane A and a page plane B and the page buffer resource is coupled to a host bus through a first port and to an internal bus through a second port, comprising:a circuit for receiving a write page buffer sequential command over the host bus and allocating the page plane A of the page buffer resource to a user mode, such that the page plane A is accessible over the host bus in the user mode; a circuit for receiving a write data block over the host bus and transferring the write data block to the page plane A; a circuit for receiving a program with page buffer command and allocating the page plane A to a flash array controller mode, such that the page plane A is accessible by a flash array controller over the internal bus in the flash array controller mode; and a circuit for receiving a swap page buffer command over the host bus, and swapping the user mode and the flash array controller mode between the page plane A and the page plane B.
 20. A computer system, comprising:a central processing unit configured to transfer a command and a write data block over a host bus; and a flash memory device having a page buffer resource coupled to the host bus through a first port and to an internal bus through a second port, the flash memory device configured to (1) receive the command over the host bus and to allocate the page buffer resource according to the command, and (2) receive and buffer the write data block in the page buffer resource while loading another write data block into a flash cell array; a flash array controller circuit coupled to the internal bus; and an interface circuit coupled to the host bus and to the page buffer circuit, the interface circuit configured to receive the command and to generate a control signal to allocate page planes of the page buffer resource to user and flash array controller modes according to the command.
 21. The computer system of claim 20, wherein the command comprises a write page buffer sequential command, the write page buffer sequential command causing the interface circuit to allocate a first page plane of the page planes to the user mode and receive the write datablock over the host bus and transfer the write data block into the first page plane.
 22. The computer system of claim 21, wherein after the write page buffer sequential command is received, the command comprises a program with page buffer command, the program with page buffer command causing the interface circuit to allocate the first page plane to the flash array controller mode.
 23. The computer system of claim 22, wherein if a second page plane of the page planes is not allocated to the flash array controller mode, the interface circuit allocates the second page plane to the user mode and receives a next write page buffer sequential command and a next write data block over the host bus and transfers the next write data block into the second page plane.
 24. The computer system of claim 20, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a write page buffer sequential command, such that the interface circuit allocates the page plane A to the user mode and receives the write data block over the host bus and transfers the write data block into the page plane A.
 25. The computer system of claim 24, wherein a subsequent command received over the host bus comprises a program with page buffer command, such that the interface circuit allocates the page plane A, to the flash array controller mode.
 26. The computer system of claim 25, wherein the interface circuit allocates the page plane B to the user mode if the page plane B is not allocated to the flash array controller mode.
 27. The computer system of claim 20, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a write page buffer sequential command, such that the interface circuit allocates the page plane B to the user mode and receives the write data block over the host bus and transfers the write data block into the page plane B.
 28. The computer system of claim 27, wherein a subsequent command received over the host bus comprises a program with page buffer command, such that the interface circuit allocates the page plane B to the flash array controller mode.
 29. The computer system of claim 28, wherein the interface circuit allocates the page plane A to the user mode if the page plane A is not allocated to the flash array controller mode.
 30. The computer system of claim 20, wherein the page planes comprise a page plane A and a page plane B, and wherein the command comprises a swap page buffer command, the swap page buffer command causing the interface circuit to swap the user mode and the flash array controller mode between the page plane A and the page plane B.
 31. A computer system, comprising:a central processing unit configured to transfer a command and a write data block over a host bus; a page buffer resource having a first port and a second port and being coupled to the host bus through the first port; a circuit coupled to the host bus and to the second port of the page buffer resource, the circuit configured to receive the command and to allocate the page buffer resource to receive and buffer the write data block while loading another write data block into a flash cell array, the circuit comprising a circuit for receiving a write page buffer sequential command over the host bus and allocating a first page plane of the page buffer resource to a user mode such that the first page plane is accessible over the host bus in the user mode, a circuit for receiving the write data block over the host bus and transferring the write data block to the first page plane, and a circuit for receiving a program with page buffer command and allocating the first page plane to a flash array controller mode such that the first page plane is accessible by a flash array controller over the internal bus in the flash array controller mode; and a circuit for allocating a second page plane of the page buffer resource to the user mode if the second page plane is not allocated to the flash array controller mode.
 32. The computer system of claim 31, further comprising a circuit for receiving a second write page buffer sequential command over the host bus, and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 33. The computer system of claim 31, further comprising a circuit for programming a flash cell array with the write data block from the first page plane while receiving a second write page buffer sequential command over the host bus and receiving a second write data block over the host bus and transferring the second write data block to the second page plane.
 34. A computer system, comprising:a central processing unit configured to transfer a command and a write data block over a host bus; a page buffer resource comprising a page plane A and a page plane B, and having a first port coupled to the host bus and a second port; a circuit coupled to the host bus and to the second port of the page buffer resource, the circuit configured to receive the command and to allocate the page buffer resource to receive and buffer the write data block while loading another write data block into a flash cell array, the circuit comprising a circuit for receiving a write page buffer sequential command over the host bus and allocating the page plane A of the page buffer resource to a user mode such that the page plane A is accessible over the host bus in the user mode, a circuit for receiving the write data block over the host bus and transferring the write data block to the page plane A, and a circuit for receiving a program with page buffer command and allocating the page plane A to a flash array. 